Adjustment arrangements such as those in question here are used, for example in motor vehicles, for driving electrical window winders or sunroofs, but other applications are also possible, such as electrical tailgates, sliding doors, etc. In order to increase the convenience in use and safety, pulse width modulated motor activation is often used in connection with such adjustment arrangements, said pulse width modulated motor activation being intended to ensure synchronized operation of the motor even when there are fluctuations in the on-board system voltage, generally in the supply voltage. Such PWM activation is also advantageous in conjunction with conventional anti-trap systems.
Specifically, closed-loop control of the adjustment speed is also enabled with such PWM activation means, in addition to synchronized operation of the motor being ensured, in the event of fluctuations in the supply voltage, in order to provide increased allowed reaction time by virtue of slower closing speeds, for example, and similar advantages for an anti-trap system. This is particularly relevant in the 25 mm range of the FMVSS 118 guideline, in accordance with which anti-trap systems with a spring rate of 65 N/mm are tested. In particular, even when a sliding roof is closed, for example, the closing speed can be reduced prior to said sliding roof entering the seal, with energy being taken from the moved mechanical system. In the ideal case, it is possible in this way to dispense with a mechanical damping element.
In the known technologies, electronic controllers are used for this purpose, said controllers calculating the required duty factor by measuring the on-board system voltage of the motor vehicle in order to make available the desired motor voltage (for example 70% of the on-board system voltage in specific time intervals). If appropriate, the motor voltage can then be checked, i.e. measured back, with the result that a closed control loop is produced. In this way, on-board voltage fluctuations can be corrected. However, fluctuations in the synchronized operation of the respective adjustment arrangement, for example a window winder or a sliding roof, still occur, with these fluctuations in the synchronized operation resulting from different mechanical loads, in particular as a result of the different component parts which engage or become disengaged in the course of an adjustment movement depending on the position (or time) in the mechanical system. These fluctuations in the synchronized operation as a result of varying mechanical forces are not corrected in the known systems since fluctuations in the synchronized operation represent the input or measurement signal of the anti-trap algorithm. As a result, the convenience for the user is reduced and the advantages of the PWM activation for the anti-trap system are reduced.